DE 10 2004 050 747 A1 and the as yet unpublished German patent application DE P 10 2005 045228.0-44 disclose coating compositions of the type specified at the outset which comprise adducts with alkoxysilane functionality. The coating compositions described therein are cured using suitable catalysts, to form Si—O—Si networks. One of the applications of the coating compositions is as clearcoats in OEM systems. They lead to coatings having very high scratch resistance, but are frequently in need of further improvement in terms of weathering stability and in terms of cracking, more particularly at relatively high coat thicknesses of more than 40 μm. A further disadvantage is the decidedly high price of the adducts with alkoxysilane functionality, that are included in decidedly large quantities in these coating compositions.
US 2006-0217472 A1, furthermore, discloses that the scratch resistance of polyurethane-based coatings can be improved by taking coating compositions which comprise a hydroxyl-containing binder, a crosslinker containing isocyanate groups, and a metal catalyst for the OH/NCO reaction and adding to them an aminosilane, such as bis(3-propyl-trimethoxysilyl)amine, or its reaction products with isocyanates. Modifying the aminosilanes with surface-active components, however, is not described in US 2006-0217472 A1.
Furthermore, the as yet unpublished American patent application with the Ser. No. 11/227,867, of Sep. 15, 2005, describes coating compositions which comprise reaction products (I) of a dimer fatty acid diol with an isocyanatoalkyltrialkoxysilane.
A particular feature of the coatings obtained using these coating compositions is a very high gloss. As the fraction of the reaction products (I) of the dimer fatty acid diol with the isocyanatoalkyltrialkoxysilane in the coating compositions goes up, the hardness and the resistance to solvents, as measured in double rubs with methyl ethyl ketone, goes down. In the field of automotive finishing, however, the demand is increasingly for coatings having an improved hardness and resistance and hence an improved scratch resistance.
WO01/98393 discloses coating compositions featuring enhanced adhesion to aluminum substrates, and comprising not only a hydroxyl-containing binder and an isocyanato-containing crosslinker but also a silane oligomer (B) having at least two isocyanate groups, as an essential constituent, said oligomer (B) being the reaction product of an isocyanate-functional compound (A) with a coupling reagent (X) which contains at least one alkoxysilane-functional group and at least one group that is reactive toward isocyanate groups. Modifying the silane oligomers (B) with surface-active components is likewise not described in WO01/98393. This application exploits the known property of silanes of entering into particularly strong bonds with aluminum. In order to achieve particularly effective adhesion, indeed, it is of advantage if the silanes used tend to accumulate at the interface with the substrate. Furthermore, in the coating compositions it describes, an added catalyst for the crosslinking of the silane groups is absent.
WO 01/09260, furthermore, discloses coating compositions which comprise polysiloxanes (a) having at least one reactive group, compounds (b) which have at least one group reactive with the reactive groups of the polysiloxanes, and, if appropriate, particles (c), and further constituents. In the curing reaction, therefore, the polysiloxanes do not form an Si—O—Si network with the compounds (b).
EP-B-1 204 701 describes coating compositions which as well as nanoparticles comprise a surface-active substance, whereby an accumulation of the nanoparticles at the surface comes about in the coating, leading to improved scratch resistance on the part of the coatings. The extent of such structures is usually low, similar to a chain of beads on the surface.
Owing to the extremely strong interparticulate interactions and to the usually incomplete stabilization of the particles, however, there are frequent instances of particle agglomeration and hence an adverse effect on the leveling and the appearance of the resulting coatings. Furthermore, extremely effective stabilization of the particles is necessary in order to ensure a wide processing window and to avoid possible deposits in the circulation lines.
WO05/028550, furthermore, discloses functional polymers which are prepared by treating bulk polymers with a surface modifier additive (called “SMA” for short). These surface modifier additives are polymers having a functional block which has a surface-active segment. These modified polymers are blended with the unmodified bulk polymers, and the resulting blends are used to produce moldings or similar articles or to produce coatings, in order to exert targeted control over the properties of the surfaces of the articles or coatings obtained. The surface-active modification of individual constituents of a coating composition which is crosslinked only thereafter to give a coating having targeted surface properties is not, however, described in WO05/028550.
Furthermore, the polymers described in WO05/028550 are employed for biological or medical applications, such as for cosmetics, for the biocidal treatment of gloves, clothing, medical instruments, and the like, or for the biocidal finishing of air filters and the like, and also for the production of diagnostic chips, by bioactive surface treatment of the chips.
The descriptions do include descriptions of alkoxysilane-functional, surface-active moldings and coatings where the bulk polymers are treated in some cases with polymeric additives which have alkoxysilane groups. The curing of the alkoxysilane groups in those cases is by a number of hours of moisture treatment or by treatment with aqueous acids. This treatment, which is typical in the field of plastics parts, however, is associated with considerable additional cost and inconvenience in the field of automotive finishing, and is therefore undesirable. Moreover, clearcoat materials that are typically employed in the field of automotive finishing are generally incompatible with the aqueous acids required, meaning that it is not possible to transpose the functional coatings described in WO05/028550 to the field of automotive finishing.
EP-B-1 295 914, finally, discloses coating compositions featuring an enhanced oil and water repellency effect, these compositions comprising an alkoxysilyl-functional acrylic resin, an acrylic resin containing alkoxysilyl groups and secondary dimethylpolysiloxane chains, a hydroxyl- and epoxy-functional acrylic resin, and a polyester resin having a high acid number. On curing of the coating compositions, unwanted Si—O—C nodes may form in competition with the desired Si—O—Si nodes, as a result of reaction of the —Si(O-alkyl)3 groups with the hydroxyl groups of the alkyl(meth)acrylate resins, the Si—O—C nodes being hydrolytically labile and leading to reduced chemical resistance on the part of the resulting coating. Since the heavy-duty OEM clearcoats are to have as high a weathering resistance as possible, it is a concern that, as compared with polyurethane networks, the poly(meth)acrylate networks exhibit a reduced weathering resistance.
Furthermore, in the case of acrylate binders prepared via free radical polymerization, the relatively broad molecular weight distribution means, very generally, that the formulation of 1 K [one-component] clearcoat materials with solids contents significantly higher than 50% by weight is possible only at great cost and inconvenience. At higher proportions, the coating materials are difficult to process, on account of their high viscosity.
The problem addressed by the present invention was therefore that of providing coating compositions which lead to coatings having a high micropenetration hardness and a very good dry scratch resistance, typically determined in the crockmeter test. A further problem addressed by the invention was that of providing coating compositions which lead to a highly weathering-stable and crack-resistant network. Advantageously, furthermore, the network ought to possess polyurethane units and/or polyurea units to a high degree, with the unwanted formation of Si—O—C and of Si—N—C nodes being very largely suppressed. The coating compositions ought additionally to meet the requirements typically imposed in the field of automotive OEM finishing. The coating compositions ought therefore in particular to exhibit good haze, i.e., no haze, good leveling, and a very good overall visual appearance. Finally the desired properties ought to be obtained as inexpensively as possible.